This specifies a little the scope of the variable to make it
more realistic with the actual values it may have. We do have
a static typed compiled language, why don't we use it?
Save them in extra properties from folder container.
This is required because the client once a request is accepted
or denied sets these two properties and save the message again.
As we cannot modify an IMAP message, we use this utility.
See [MS-OXSHARE] Section 3.1.4.3 for details.
It acts as a proxy of MAPIStoreMailMessage and it manages the properties
defined in [MS-OXSHARE] Section 2.2 by storing them in the mail message
as eXtensible MIME headers which starts with X-MS-Sharing.
